1. Field of the Invention
The present invention relates to a new gene that encodes a transcription factor induced by water deficit conditions and abscisic acid from Helianthus annuus, having a homeodomain associated to a leucine zipper. The transcription factor is useful to be cloned in DNA constructions for transforming host cells and plants. The transgenic plants comprising the transcription factor are resistant to harmful environment conditions such as the water deficit stress and high salinity. A nucleic acid promoting sequence is also provided wherein the sequence is inducible by water deficit or abscisic acid, constructions, host cells and transgenic plants that comprise the sequence.
2. Description of the Prior Art
The homeodomain is a 60 amino acid motif present in a number of eukaryotic transcription factors involved in developmental processes (Gehring, Science 236, 1245-1252, 1987). Genes containing homeoboxes have been isolated from many eukaryotic organisms including fungi, mammals and plants (Gehring, W. J., et al., Annu. Rev. Biochem. 63, 487-526, 1994). Plant homeoboxes can be divided into several families according to sequence conservation and structure in and outside the homeodomain (Chan, R. L., et al. Biochim. Biophys. Acta 1442 (1), 1-19, 1998). Members of one of these families have a distinct feature: they code for proteins termed Hd-Zip, because they contain an homeodomain associated with a leucine zipper, a coiled-coil structure involved in dimerization. Hd-Zip proteins bind DNA efficiently only as dimers (Sessa, G., et al., EMBO J. 12, 3507-3517, 1993; Palena C. M., et al., Biochem J. 341, 81-87, 1999). It has been suggested that these proteins may be involved in regulating developmental processes associated with the response of plants to environmental conditions (Chan, R. L., et al. Biochim. Biophys. Acta 1442 (1), 1-19, 1998, Carabelli, M., et al., Plant J. 4, 469-479, 1993; Schena, M., et al., Genes Devel. 7, 367-379, 1993). One of the most common environmental stresses to which plants are exposed is dehydration. Although many seeds tolerate extreme dehydration, tolerance is rare in vegetative parts of the plant. Plants respond to water stress with the expression of a specific set of genes, which allows them to adapt to the altered environmental conditions (Bray, E. A. Trends Plant Sci. 2, 48-54, 1997 y Shinozaki, K. and Yamaguchi-Shinozaki, K. Plant Physiol. 115, 327-334, 1997). The hormone abscisic acid (ABA) plays an important role in a sub-set of these responses (Shinozaki, K. and Yamaguchi-Shinozaki, K. Plant Physiol. 115, 327-334, 1997 y Leung, J. and Giraudat, J. Ann. Rev. Plant Physiol. Plant Mol. Biol. 49, 199-222, 1998).
The characterization of the promoting regions of the genes involved in the tolerance or resistance to water stress shown the existence of an element that responds to ABA, namely ABRE, and an element responding to desiccation, namely DRE.
Söderman et al. have disclosed [described] the [two] genes, ATHB-7 and -6 of Arabidopsis that is [are] induced by abscisic acid and water deficit (Söderman E. et al., The Plant Journal 10: 375-381, 1996 and Soderman E. et al. Plant Molecular Biology 40: 1073-1083, 1999). The authors have not shown that the over-expression of these genes provide tolerance to water deficit.
U.S. Pat. No. 5,981,729 discloses a new gene that is induced by water deficit and abscisic acid and that encodes a transcription factor of A. Thaliana. This patent does not discloses any reference to transgenic plants carrying the gene of the present invention and resisting to water stress conditions.